Iphone4s SMS can't be sent

Everyone can send a text message to a mobile phone, but only one person can send a text message when it shows that it is being sent, but it cannot be sent all the time. There may be the following situations:

1, there is something wrong with the other party's mobile phone number, so you can't accept SMS. Just cancel sending.

2. The number is not saved to the contact person, and the mobile phone number should be written in the mobile bar, which may not be sent out.